1. Field of the Invention
The present invention generally relates to a current collector for a bipolar secondary battery. In particular, the present invention relates to an improvement for suppressing a temperature increase of a bipolar secondary battery.
2. Background Information
In recent years, from the perspective of the environment and fuel consumption, hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles are being manufactured and sold, and new research continues. In such so-called electric powered vehicles, use of a power source device that can be charged and discharged is indispensible. Such secondary batteries as lithium ion batteries and nickel chloride batteries and electric double layer capacitors are used as this power source device. In particular, due to their high energy density and high durability with respect repeated charging and discharging, lithium ion secondary batteries are considered well-suited to electric powered vehicles and various development avenues are being diligently pursued. In order to employ a secondary battery as a power source for driving a motor in any of the aforementioned electric powered vehicles, it is necessary to use a plurality of the secondary batteries connected together in series to secure a large output.
However, when batteries are connected through connecting parts, the output declines due to an electrical resistance of the connecting parts. Also, batteries having connecting parts are disadvantageous spatially. That is, due to the connecting parts, declines of the output density and the energy density are incurred.
Bipolar lithium ion secondary batteries and other bipolar secondary batteries have been developed as ways to solve this problem. The bipolar secondary batteries have an electric power generating element comprising a plurality of bipolar electrodes stacked with electrolyte layers in-between, the bipolar electrodes each comprising a positive electrode active material layer formed on one surface of a current collector and a negative electrode active material layer formed on the other surface. In other words, the bipolar secondary battery has a structure in which a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer form one single cell layer and the single cell layers are stacked in series with current collectors in-between.
In recent years, regarding such bipolar secondary batteries, technologies have been developed that lighten the weight of the current collectors and improve an output density per unit weight of the battery by including a macromolecular material in the current collectors (e.g., Japanese Laid-Open Patent Publication No. 2006-190649).